The present invention relates to the control of Volatile Organic Compounds (VOC""s) and more particularly to the removal of such compounds from an airstream and the subsequent collection or destruction of the compounds.
Airstreams incorporating Volatile Organic Compounds are significant environmental hazards which must be cleaned or stripped of these compounds before general release into the atmosphere. The use of activated carbon as a medium for the removal of such VOC""s has become well known. Typically, the contaminated airstream is passed through and in intimate contact with activated carbon resulting in the adsorption of the VOC""s and the xe2x80x9ccleansingxe2x80x9d of the airstream. The VOC""s may then be removed from the activated carbon by desorbing the VOC""s therefrom and either collecting the compounds for possible reuse in a processing environment or destroying the compounds through oxidation or other means.
A prior art VOC control/solvent recovery system is described in U.S. Pat. No. 5,676,738 wherein a fluid bed adsorber is shown utilizing synthetic pyrolized spherical adsorbent material moving in a counter-direction to incoming contaminated gases incorporating VOC""s. The counter-flowing adsorbent beads and contaminated gas assures intimate contact between the gas and the surfaces of the adsorbent material. The resulting adsorption cleanses the airflow permitting the cleaned air to be exhausted to the atmosphere. The contaminated adsorbent material is then transported to a desorber wherein the VOC material is stripped from the adsorbent material and either condensed for reuse or destroyed in an oxidizer. After substantial use, the efficiency of adsorption is greatly reduced by the continuous adsorption and desorption performed by the adsorption material. In the U.S. Pat. No. 5,676,738 patent the adsorbent material is a synthetic pyrolized spherical adsorbent identified therein as a material known as xe2x80x9cAMBERSORBxe2x80x9d. Activated carbon beads other than the material identified above are similarly used in VOC removal processes. In all cases, the adsorbent material becomes less efficient in the respective adsorption process through continued use and reuse. The effectiveness of the adsorbent material can be renewed by reactivating the carbon; that is, in prior art VOC removal adsorbing systems, the adsorbent may be removed and subjected to reactivation conditions. The reactivated adsorbent may then be replaced and the system restarted. The requirement for shutting down the VOC removal system to permit the adsorbent to be reactivated is a major expense and limitation of such systems since the shut down of the system requires either an alternate VOC removal system during the adsorbent removal and resupply or the complete shut down of the system from which the contaminated airstream or influent gas is obtained. Efficient continuous operation of systems such as those described in U.S. Pat. No. 5,676,738 can be adversely affected by the requirement to reactivate the adsorbent used in the system.
It is therefore an object of the present invention to provide a VOC removal or destruction system using activated carbon adsorbents wherein the system can reactivate the adsorbent.
It is also an object of the present invention to provide a VOC removal or destruction system wherein contaminated adsorbent material is regenerated through the utilization of direct electric heating.
It is also an object of the present invention to provide a VOC removal or destruction system wherein contaminated adsorbent material is regenerated through the controlled application of direct electric heating in a cylindrical ceramic heater region within a desorber and wherein the temperature used for the direct electric heating is under program control.
It is a further object of the present invention to provide a VOC removal or destruction system wherein adsorbent material may be regenerated through the application of direct electric heating and wherein the material may be reactivated through application of the same direct electric heating under the control of the programmable controller.
It is still another object of the present invention to provide a VOC removal or destruction system wherein adsorbent materials such as activated carbon can be regenerated and/or reactivated under program control.
It is another object of the present invention to provide a VOC removal or destruction system incorporating a desorber for regenerating contaminated activated carbon through direct electric heating and the passage of an inert gas and wherein the temperature of heating can be increased together with the addition of water or steam to reactivate the activated carbon.
It is still another object of the present invention to provide a VOC removal or destruction system wherein contaminated carrier gas from a desorber is supplied to an oxidizer for oxidizing the VOC""s.
It is still another object of the present invention to provide an oxidizer for use in a VOC removal or destruction system wherein the products of combustion of a selected fuel includes an inert gas for supply to the desorber for use as a carrier gas.
It is still another object of the present invention to provide an oxidizer for use in a VOC removal or destruction system wherein the products of combustion of a selected fuel includes an inert gas for supply to the desorber for use as a carrier gas and wherein the temperature of said combustion is sufficient to energize the oxidation process to oxidize the VOC""s contained in the contaminated carrier gas.
These and other objects of the present invention will become apparent to those skilled in the art as the description proceeds.
The present invention incorporates a system for removing VOC""s from a contaminated gas stream. The VOC""s are removed from the gas stream in any convenient manner and in accordance with prior art techniques. For example, the VOC""s may be removed through the use of an adsorber wherein the contaminated gas comes into intimate contact with an adsorbent material such as activated carbon; the VOC""s are adsorbed by the material and the clean gas is exhausted into the atmosphere. The contaminated adsorbent material is supplied to a desorber and passed through a cylindrical ceramic tube in contact with spaced electrodes. Electrical power is supplied to the electrodes to generate direct electric heating of the contaminated adsorbent material. An inert gas is passed through and around the adsorbent material to strip the VOC""s from the material. The adsorbent material, thus regenerated, is returned to the adsorber for further operation in the removal of VOC""s from a contaminated airstream.
The contaminated carrier gas is supplied to an oxidizer and subjected to a temperature sufficient to oxidize the VOC""s. The oxidizer includes a burner supplied with a chosen fuel and combustion air. The combustion is stoichiometric and at a sufficient temperature to oxidize the VOC""s; however, a portion of the resulting combustion gases of the stoichiometric combustion are directed from the oxidizer to the desorber as an inert carrier gas. This return of the carrier gas may be temperature controlled and may include a provision for the injection of water or steam to enable the desorber, in combination with the programmed higher temperature of the ceramic tube, to act as a reactivation chamber for reactivating the adsorbent material.